1. Field of the Invention
The present invention relates to various methods and apparatus for detecting environmental conditions around perishable merchandise and visually relating this information in an easily read format as the environmental conditions relate to the fitness for use or spoilage of the merchandise. These embodiments can be used to detect the fitness for use of long shelf-life products such as ammunition, fuel, and other products which can have shelf-lives of up to 30 or more years as well as detecting the likelihood of spoilage in short shelf-life products such as chilled foodstuffs such as meats, vegetables, and other similar frozen foods as well as medicines and other items which have shelf-lives of hours or days if exposed to improper environmental storage conditions.
The monitoring and control of environmental conditions around all products can give them enhanced, but not indefinite shelf-life by controlling the environmental conditions around them such that these environmental conditions decrease the risk of the products becoming defective or spoiled over time. More particularly, health concerns for spoiled food have recently led several governments to suggest or require that all food requiring refrigeration for transport or storage be continually monitored to minimize the risk of spoilage due to exposure to increased temperatures.
One of the dangers involved in food transport is the danger of the growth of bacteria such as Clostridium Botulinum which produces botulinum toxins in food. Traditionally it was easy for consumers to tell if food was at a higher risk of being spoiled by its smell, look and feel. However, changes in the smell, look and feel of food are caused principally by exposure to oxygen, ultraviolet light, or both not by the bacteria which can lead to food poisoning. With the advent of modern day packaging and refrigeration most foods are not exposed to a sufficient amount of oxygen or ultraviolet light to make the food consumers buy obviously spoiled with traditional means.
Since most bacteria can grow on food in the absence of oxygen, the only sure method of preventing their growth is to maintain the food at or below a specified temperature, typically at or below between 32-33 degrees Fahrenheit or 0 to 0.5 degrees Celsius. Even a small temperature rise to 34 or 36 degrees or 0.5-2 degrees Celsius, over a few days, can allow C. Botulinum bacteria to grow in sufficient numbers to cause food poisoning. By continuously monitoring the environmental temperature around food, the present invention can easily determine the conditions when the food is likely to have become spoiled.
Temperature is not the only environmental factor that can affect the usefulness of products. The Relative Humidity, or the vapor pressure of water in the atmosphere around the product, can expose the product to an excessive amount of water which may degrade certain products including but not limited to potato chips, crackers, bread, pasta, vegetables, meats, and other food products.
The present invention can be used to monitor the humidity and temperature of the environment around a product which can both affect the usefulness and shelf-life of other products such as ammunition, fuel, and other products. Typically ammunition has a shelf-life of 20 years or more. However, this shelf-life can be lowered by exposure to excessive temperatures as well as humidity. Use of the present invention will provide a rapid, visual indication of the fitness for use of ammunition that has been in storage for many years.
Prolonged exposure to high heat and humidity accelerates the aging process and reduces the service life of many products, both military and commercial. Administratively tracking environmental exposures is an impossible task for items with long life cycles. Tracking ordinance offers a significant challenge, since it may be loaded or transferred in a multitude of environments and ultimately stored for many years on land or at sea. Currently, as ordinance is shipped, transferred, and mixed with various stock, its relative freshness can only be determined by age when, in fact, age only plays a minor role in the overall freshness. Application of sensing devices would allow the freshest ammunition/ordinance to be reserved for the most critical situations.
The present invention provide a means to track the relative fitness for use of a wide variety of class of goods without the use of any electronic means, although it should be apparent to those skilled in the art that electronic means can be incorporated into the present invention for use in an inventory tracking system as described below.
2. Background Art
Generally a temperature sensitive product does not decay or become spoiled as a result of exposure to a given temperature. Instead, the product spoils due to the amount of heat imparted to it as a result of a temperature difference over time. The present invention is distinguished over the prior art by its use of shape memory material, and specifically shape memory polymers, to cumulatively track a products exposure to various environmental conditions over time, indicating the degree of deterioration based on this exposure, and doing so cheaply, accurately, and without the aid of any electrical device.
First introduced in the United States in 1984, Shape Memory Polymers (hereinafter “SMPs”) are polymers whose qualities have been altered to give them dynamic shape “memory” properties. SMPs are polymers that derive their name from their inherent ability to return to their original “memorized” shape after undergoing a shape deformation. An article in the Journal of Food Protection (Vol. 61. No. 9. 1998. Pages 1154-1160) entitled “Conservative Prediction of Time to Clostridium Botulinum Toxin Formation for Use with Time-Temperature Indicators to Ensure the Safety of Foods” authored by Guy Skinner and John Larkin outlines the need for a sensor technology such as the one CRG is currently developing. Specifically, this paper outlines an entire market for CRG's technology. This market is commonly known as the Larkin market.
In summary, the Larkin market involves foods that are packaged in varying forms of reduced oxygen packaging (hereinafter “ROP”). ROP creates an environment that significantly reduces the growth of anaerobic spoilage organisms. This enables longer shelf life for fresh foods and increases the market range for certain fresh foods that are geographically disadvantaged such as seafood. This market considers foods that are not frozen to be fresh foods. Fresh foods are considered premium and consumers are willing to pay a premium price; therefore, the margins associated with this fresh food segment of the consumer foods industry are much higher.
There is a fine line between frozen food temperatures and slightly warmer temperatures that enable the growth of deadly toxins as described in Larkin's article. Lethal levels of botulinum toxins can result if fresh foods are subjected to temperatures above 3.3° C. for relatively long periods of time. Moreover, if the fresh foods have been packaged in ROP is becomes difficult for the average consumer to detect because the lack of oxygen, which is not necessary for the bacteria growth, will mask some of the common visual spoilage signs such as odor, slime, and texture.
Because foods such as seafood may be packaged and repackaged several times between the dock and the supermarket, it becomes difficult to determine if the seafood is always fresh and each link of the chain accepts a significant liability for the quality of the entire chain. The present invention eliminates the risk and liability issues associated with this market, and reduce consumer related death rates ultimately reducing insurance rates and increasing profit for the associated businesses as any spoilage or deteriorated products are typically paid for by the seller of the goods.
All SMPs have at least one transition temperature (hereinafter “Tg”) at which point the SMP transitions between a hard rigid plastic to a soft, pliable, elastomeric polymer. When the SMP is above its Tg it is soft, when below its Tg it is hard. Once the temperature of the SMP is above its Tg the SMP can generally be deformed into the desired shape. The SMP must be cooled below its Tg while maintaining the desired deformed shape to “lock” in the deformation. Once the deformation is locked in, the polymer network cannot return to its “memorized,” or original shape due to thermal barriers. The SMP will hold its deformed shape indefinitely until it is again heated above its Tg, when the SMP stored mechanical strain is released and the SMP returns to its “memorized” shape. It is important to note that the Tg represents the average temperature at which a material transitions from a rigid polymer to an elastomeric polymer. Because it is an average temperature the polymer can sometimes exhibit limited shape memory recovery below the Tg. Typically this limited recovery is small enough and occurs close enough to the Tg that it does not affect the function for which the SMP is designed.
While heated above its Tg, the SMP has the flexibility of a high-quality, dynamic elastomer, tolerating up to 400% or more elongation; however, unlike normal elastomers, SMP can be reshaped or returned quickly to its memorized shape and subsequently cooled into a rigid plastic a change that can be repeated without degradation of the material
The SMP transition process is a thermo-molecular relaxation rather than a thermally-induced crystalline phase transformation, as with shape memory alloys (hereinafter “SMAs”). In addition, SMPs demonstrates much broader range and versatility than SMA in shape configuration and manipulation.
SMPs are not simply an elastomer, nor simply a plastic. They exhibit characteristics of both materials, depending on its temperature. While rigid, SMP demonstrates the strength-to-weight ratio of a rigid polymer; however, normal rigid polymers under thermal stimulus simply flow or melt into a random new shape, and they have no “memorized” shape to which they can return. While heated and pliable, SMP has the flexibility of a high-quality, dynamic elastomer, tolerating up to 400% or more elongation; however, unlike normal elastomers, SMP can be reshaped or returned quickly to its memorized shape and subsequently cooled into a rigid plastic. Depending on the type of SMP used the activation temperature is customizable to between −30° F. and 520° F. (−40° C. to 270° C.).
There are three types of thermally activated SMP: 1) partially cured resins, 2) thermoplastics, and 3) fully cured thermoset systems. There are limitations and drawbacks to the first two types of SMP. Partially cured resins continue to cure during operation and change properties with every cycle. Thermoplastic SMP “creeps,” which means it gradually “forgets” its memory shape over time. A thorough understanding of the chemical mechanisms of involved will allow those of skill in the art to tailor the formulations of SMP to meet specific needs.
Several known polymer types exhibit shape memory properties. Probably the best known and best researched polymer type exhibiting shape memory polymer properties is polyurethane polymers. Gordon, Proc of First Intl. Conf. Shape Memory and Superelastic Tech., 115-120 (1994) and Tobushi et al., Proc of First Intl. Conf. Shape Memory and Superelastic Tech., 109-114 (1994) exemplify studies directed to properties and application of shape memory polyurethanes. Another polymeric system based on crosslinking polyethylene homopolymer was reported by S. Ota, Radiat. Phys. Chem. 18, 81 (1981). A styrene-butadiene thermoplastic copolymer system was also described by Japan Kokai, JP 63-179955 to exhibit shape memory properties. Polyisoprene was also claimed to exhibit shape memory properties in Japan Kokai JP 62-192440. Another known polymeric system, disclosed by Kagami et al., Macromol. Rapid Communication, 17, 539-543 (1996), is the class of copolymers of stearyl acrylate and acrylic acid or methyl acrylate. Other SMP polymers known in the art includes articles formed of norbornene or dimethaneoctahydronaphthalene homopolymers or copolymers, set forth in U.S. Pat. No. 4,831,094.
The primary design components of thermally activated SMPs include at least one monomer, possibly a co-monomer, a crosslinker, and possibly an initiator and additional filler material. A polymer engineered with shape memory characteristics provides a unique set of material qualities and capabilities that enhance traits inherent in the polymer system itself. SMPs can be chemically formulated with a transition temperature to match any application need. It can be cast and cured into an enormous variety of “memorized” shapes, from thick sheets and concave dishes to tiny parts or a complicated open honeycomb matrix.
There are other methods besides thermal energy to activate the shape memory properties of SMP. Radiation, UV light, Magnetism, can be used to activate the SMP. Throughout this application “activation” is defined as transitioning the material from a hard rigid state to a soft pliable state. Additionally throughout this application “deactivation” is defined as transitioning the material from a soft pliable state to a hard rigid state.
Water activated SMP is a thermally activated SMP. As water is absorbed by the SMP this absorption of water lowers the thermal activation temperature such that the SMP will return to its memorized shape at a lower Tg than it would have had it not absorbed the water.
Many articles have been published recently describing this phenomenon. See Chen, et. al. Thermosetting Polyurethanes with Water-Swollen and Shape memory properties, Journal of Applied Polymer Science Vol 84 1504-1512 (2002); Huang, et. al, Water-driven Programmable polyurethane shape memory polymer: Demonstration and mechanism, Applied Physics Letters 86, 114105 (2005); Yang, et. al., Qualitative separation of the effects of carbon nano-powder and moisture on the glass transition temperature of polyurethane shape memory polymer, Scripta Materialia 53 105-107 (2005); and Yang, et. al., Effects of moisture on the glass transition temperature of polyurethane shape memory polymer filled with nano-carbon powder, European Polymer Journal 41 1123-1128 (2004).
Shape memory polymer material is the critical enabling technology for the present invention. Multiple corporations provide various SMP materials for various applications. Among them are (a) Composite Technology Development, Inc. (Lafayette, Colo.) www.ctd-materials.com; (b) ILC Dover LP (Frederica, Del.) www.ilcdover.com; (c) mnemoScience GmbH (Aachen, Germany) www.mnemoscience.com; and (d) Mitsubishi Heavy Industries, Ltd. (Nagoya, Japan) www.mhi.co.jp; and (e) Cornerstone Research Group Inc. (Dayton, Ohio) www.crgrp.com. Of the above those from Cornerstone Research Group Inc. are particularly preferred.
Shahinpoor et al, U.S. Pat. No. 5,735,067 discloses a temperature sensor having an indication surface, at least one SMA member with a first shape at temperatures below a critical temperature and a second shape at temperatures above the critical temperature, and a plurality of indicators mounted with the members which obscure the indication surface when the members are in the first shape, and do not obscure the indication surface when the members are in the second shape. The shape change of the SMA element causes the sensor to change between two readily distinguishable states to indicate that a temperature threshold was exceeded, and must always be maintained at a temperature below the transformation temperature of the SMA member(s) until the beginning to the sensing operation.
Akers, U.S. Pat. No. 6,848,390 disclosure a cumulative thermal exposure monitor having a fluid sealed inner cavity and a thermally responsive member formed of a shape memory material which moves an indicator. The housing, cavity, and shape memory material transition temperature ranges are calibrated relative to one another such that the shape memory material gradually changes from one shape to another depending on the environmental temperature.
Akers essentially uses a variety of materials to insulate the shape memory material from the environment to control the amount of thermal energy it absorbs. Shahinpoor uses SMA to indicate a single threshold temperature has been crossed. The device disclosed by Akers does not allow for sudden temperature changes as the time needed for the temperature changes in the outside environment to reach the shape memory material prevents its movement. Additionally the cost necessary to balance the insulation, housing and other material for each situation is expensive and time consuming. Likewise the device disclosed by Shahinpoor can only tell if a single threshold temperature has been crossed, not if a cumulative exposure to a lower temperature has spoiled or made unfit for use a material.
Debord et al, U.S. Pat. No. 7,057,495 discloses an electronic assembly contained in a label that performs time-temperature integration (hereinafter “TTI”) and indicates that time and/or temperature levers have been reach that will compromise the safety or shelf-life of an item. The principal drawback with this method is that the sensor must have electricity to run. The current devices do not need electricity to monitor the environmental conditions around them.
Other technologies exist that are used for passive temperature sensing. The major technologies that are used for these devices are 1) chemical diffusion to show color change and 2) heat transfer to enact a change in polymer modulus. Products such as Checkpoint® labels (http://www.vitsab.com/) that use chemical diffusion technology are low profile and can be easily integrated into packaging. However, their resolution in interpreting freshness for some markets is under debate and remains a barrier to widespread acceptance. Time Temperature Integration, LLC products use controlled heat transfer and polymer modulus change to indicate freshness. This product is bulkier than the chemical diffusion labels; however, the resolution of the TTI is better throughout the desired time period. Both technologies have limitations in their resolution and design flexibility when compared to SMP-based sensors.
Therefore there is a need in the field for a cheap method to easily and quickly identify a material that is unfit for use due to deterioration or spoilage because of exposure to certain environmental conditions. The present invention overcomes these limitations by providing a cheap, easy to use, visual indication of the fitness for use or spoilage of an item.